Device and method for manufacturing a preform for optical fibres by chemical vapour deposition

ABSTRACT

A method and device for manufacturing a preform for optical fibres through chemical deposition on a substrate for deposition arranged vertically. A chemical deposition chamber includes at least one gripping member rotatably mounted about an axis Z-Z and adapted to hold at least one end of at least one elongated substrate for chemical deposition for the formation of a preform. The chamber includes at least one burner which is mobile along a direction Z substantially parallel to the axis Z-Z and adapted to deposit on the elongated substrate, a chemical substance for the formation of a preform and at least one suction element for collecting exhaust chemical substances. The suction element is arranged on the opposite side of the burner with respect to the axis Z-Z and is mobile along the direction Z and is positioned at a lower height than the burner.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase application based onPCT/EP02/06778, filed Jun. 19, 2002, the content of which isincorporated herein by reference, and claims the priority of EuropeanPatent Application No. 01202444.4, filed Jun. 25, 2001 and claims thebenefit of U.S. Provisional Application No. 60/303,410, filed Jul. 9,2001.

BACKGROUND OF THE INVENTION

1.Field of the Invention

The present invention relates to a device for manufacturing a preformfor optical fibres through chemical deposition on a substrate fordeposition arranged vertically. More specifically, the invention relatesto a device for manufacturing one or more preforms for optical fibresthrough a chemical deposition process on one or more substrates fordeposition arranged vertically.

2.Description of the Related Art

As known, the methods for manufacturing optical fibre basically comprisea first process of manufacturing a preform from glass and a successiveprocess of drawing the optical fibre from the preform.

The most common processes of manufacturing preforms comprise one or morechemical deposition steps, through one or more burners, of suitablechemical substances on a cylindrical support; the chemical depositionsubstances typically comprise silicon and germanium, which are depositedin the form of oxides (SiO₂ e GeO₂).

The processes of manufacturing preforms through chemical depositionknown in the art comprise processes of the VAD (Vapor Axial Deposition)type and processes of the OVD (Outside Vapor Deposition) type.

Typically, in VAD type processes the cylindrical support is held in avertical position by a gripping member which operates on an upper end ofthe cylindrical support; the cylindrical support is made to turn uponitself so as to expose its entire surface to one or more burners whichare housed near to the lower end of the support and in such a positionas to emit a flow of reactants along a direction which is inclined at apredetermined angle, typically lying between 30° and 50°, with respectto the longitudinal axis of the support. The support is then movedupwards so as to allow substantially axial growth of the preform.

In processes of the OVD type, on the other hand, the cylindrical supportis held in a horizontal or vertical position by a pair of grippingmembers which operate on the opposite ends of the support; the supportis made to turn upon itself so as to expose its entire surface to one ormore burners mounted on a side of the support and in such a position asto emit the flow of reactants along a direction which is substantiallyperpendicular to the longitudinal axis of the support. The burner, inparticular, is mounted on a support structure equipped with a motoriseddriving member which allows the repeated movement of the burner parallelto the cylindrical support, so as to allow a substantially radial growthof the preform along all the sections of the support.

A typical process of the OVD type comprises the following steps. In afirst step a substantially cylindrical glass preform, called “corepreform”, is manufactured through deposition of the chemical substanceson the cylindrical support: such a preform is named in such a way sinceit will create the core and a more internal portion of the opticalfibre's cladding.

In a second step, the cylindrical support is taken out of the corepreform, freeing up a central hole in the preform.

In a third step, the core preform undergoes a process of desiccation andcompacting in a furnace, during which suitable gases (comprising, forexample, Cl₂) are made to flow inside the central hole in order toeliminate the hydroxide ions (—OH) and the atoms of water present in thepreform, thus obtaining a vitrified core preform which exhibits acentral hole having a smaller diameter than that of the initial preform.

In a fourth step, after having created the vacuum inside the hole, thevitrified core preform is placed in a vertical furnace in which themelting of a lower end of the preform itself is carried out. Such amelting causes the walls of the hole to collapse due to the vacuumcreated inside of it; the glass material cools down to form an elongatedcylindrical element of a predetermined diameter, which is pulleddownwards by a suitable traction device. Such an elongated cylindricalelement is then cooled down further and cut transversally at manyequidistant points so as to form a plurality of elongated elements, alsoknown as “core rods”, typically having a length greater than 1 m and adiameter of between 10 and 20 mm.

In a fifth step, each core rod is used as a substrate for a furtherchemical deposition process (known as “overcladding”) similar to that ofthe first step discussed earlier. In particular, on each core rod andthrough at least one burner, a plurality of chemical substances aredeposited (amongst which, typically, there is silicon oxide) which willthen constitute the outer portion of the optical fibre's cladding. Atthe end of the process a low-density final preform is obtained, fromwhich the optical fibre will then be drawn. Before the drawing, thelow-density final preform is desiccated and consolidated with the sameprocedures seen in the third step. In this way a vitrified final preformwhich is ready for the drawing process is obtained.

Various devices for manufacturing a glass (core or final) preform foroptical fibres through processes of the OVD type are known. Such devicestypically comprise a chemical deposition chamber inside which are housedthe gripping members of the cylindrical support constituting thechemical deposition substrate for the formation of the preform, a burnerwhich is mobile parallel to the longitudinal axis of the cylindricalsupport, and a suction hood positioned on the opposite side to theburner with respect to the cylindrical support and adapted to collectand remove the particulate and the exhaust chemical substances producedinside the chamber during the chemical deposition.

JP 11-1338 discloses a device for manufacturing a preform for opticalfibres through an OVD process comprising a pair of burners which aremobile parallel to the longitudinal axis of a support for preformformation which rotates upon itself and a suction hood provided on theopposite side to the burners with respect to the cylindrical support andalso mobile parallel to the longitudinal axis of the cylindricalsupport.

JP 2000-313625 discloses a device for manufacturing a preform foroptical fibres, comprising a plurality of burners which are adjacent theone to the other and mobile parallel to the longitudinal axis of asupport for preform formation, which support rotates upon itself. Asuction hood is provided on the opposite side to said plurality ofburners with respect to the cylindrical support; said hood also movesparallel to the longitudinal axis of the cylindrical support and insynchrony with said plurality of burners. In particular the hood and theplurality of burners are controlled by respective motors connected to asingle motion control circuit.

U.S. Pat. No. 5,211,732 discloses a device for manufacturing a preformfor optical fibres, wherein the gripping members hold the cylindricalsupport for preform formation in a vertical position and the chemicaldeposition takes place through a series of burners which substantiallyextends along the whole length of the cylindrical support and which ismade to oscillate parallel to the longitudinal axis of the support insuch a way that each burner only acts on a predetermined portion ofsupport. The device, moreover, comprises an air circulation systemcomprising a honeycomb structure arranged upstream of the cylindricalsupports and adapted to uniformly distribute, in the deposition area,the air which enters the chamber through a plurality of air suctionmembers formed on the rear wall with respect to the burners, and adiffusor arranged downstream of the cylindrical supports and adapted tosuck the air flows from inside the chamber. In particular, the honeycombstructure generates a plurality of air flows which are controlled so asto have substantially laminar flows distributed uniformly along thewhole length of the cylindrical support and substantially perpendicularto the longitudinal axis of the support itself.

JP 2001-019463 relates to a technique for producing a porous preform foroptical fibers, wherein glass particulates are blown from anoxygen-hydrogen flame burner to an horizontal axially rotating rod andare deposited thereon in a reaction vessel, and a moving stage mountedwith the burner is moved back and forth between two turning points. Anair exit having an exhaust hood is arranged on the side opposite to theoxygen-hydrogen burner with respect to the rod to discharge exhaustgases containing unreacted components, and the like, to the outside ofthe vessel. The air exit is moved in parallel to the burner via a movingstage, a guide, a motor, or the like, with a delay therefrom toefficiently introduce the exhaust gases from the burner into the exhausthood.

SUMMARY OF THE INVENTION

The Applicant has found that, during the chemical deposition process,inside the chemical deposition chamber fluid dynamic phenomena occursuch that the flow of reactants does not hit the cylindrical support ata right-angle to its longitudinal axis (ideal operating condition). TheApplicant believes that, in a vertical deposition process, it ispossible to restore such ideal operating condition by placing the hoodat a different level with respect to the burner: indeed, in such a casea suction current is created which, as opposed to the aforementionedfluid dynamic phenomena, brings the flow of reactants at a right-angleto the longitudinal axis of the cylindrical support.

The present invention relates, therefore, in a first aspect thereof, toa device for manufacturing a preform for optical fibres through chemicaldeposition on a substrate for deposition arranged vertically, comprisinga chemical deposition chamber including:

-   -   at least one gripping member rotatably mounted about a vertical        axis Z-Z and adapted to hold at least one end of at least one        elongated element constituting a substrate for chemical        deposition for the formation of a preform for optical fibres;    -   at least one burner which is mobile along a direction Z        substantially parallel to said axis Z-Z and adapted to deposit,        on said at least one elongated element, a chemical substance for        preform formation;    -   at least one suction element for collecting exhaust chemical        substances, said at least one suction element being arranged on        the opposite side to said at least one burner with respect to        said axis Z-Z and being mobile along said direction Z;        characterised in that said at least one suction element is        positioned at a different height with respect to said at least        one burner.

Advantageously, such a device allows a chemical deposition process to becarried out wherein the flow of reactants always hits the cylindricalsupport at a right-angle to its longitudinal axis (ideal operatingconditions); it is thus possible to obtain preforms with characteristicsof high uniformity and compactness.

Preferably, said at least one suction element is positioned at a lowerheight with respect to that of said at least one burner. Since the flowof reactants emitted by the burner is hotter than the surrounding air ittends to deviate upwards moving away from the ideal operating conditionwherein it hits the cylindrical support at a right-angle to itslongitudinal axis. Advantageously, by positioning the suction element ata lower height with respect to the burner the ideal operating conditionsare restored in that a downward suction current is created which tendsto oppose the rising effect of the flow of reactants and which,therefore, redirects such a flow at a right-angle to the longitudinalaxis of the cylindrical support.

Preferably, said at least one suction element is kept at a differentheight with respect to that of said at least one burner during thedeposition of said chemical substances for preform formation on said atleast one elongated element.

Preferably, the difference in height between suction element and burneris varied during the process of chemical deposition to account for thevariations in the process conditions (in particular, the temperature)which occur inside the chemical deposition chamber.

Preferably, the device of the present invention comprises a first movingsystem adapted to control the displacement of said at least one burnerin direction Z and a second moving system adapted to control thedisplacement of said at least one suction element in direction Z,wherein said first and second moving systems are kineticallyindependent. Advantageously, this makes it possible to separately andindependently control the motion of the burner and the motion of thesuction element along the direction Z, and thus to realise synchronousor asynchronous motions along such a direction according to the desiredfluid dynamic conditions inside the deposition chamber: in particular,this makes it possible to vary the height difference between suctionelement and burner during the chemical deposition process for thereasons mentioned above of optimisation of the fluid dynamic phenomenaand of control of the temperature inside the deposition chamber.

Preferably, said first and second moving systems are substantiallyequal.

Preferably, the device of the present invention comprises a third movingsystem adapted to control the displacement of said at least one burneralong a direction X substantially perpendicular to said direction Z anda fourth moving system adapted to control the displacement of said atleast one suction element along said direction X.

The movement of the suction element and of the burner along thedirection X can also be used, advantageously, during maintenanceoperations to facilitate the access and mobility of the operators insidethe chemical deposition chamber.

Preferably, said third and fourth moving systems are kineticallyindependent. Advantageously, this makes it possible to separately andindependently control the motion of the burner and the motion of thesuction element along the direction X, and thus to realise synchronousor asynchronous motions along such a direction according to the fluiddynamic conditions desired inside the chemical deposition chamber.

Preferably, said third and fourth moving systems are substantiallyequal.

In a second aspect thereof, the present invention relates to a methodfor manufacturing a preform for optical fibres, comprising the followingsteps:

-   -   supporting at least one substrate for chemical deposition in a        vertical position along an axis Z-Z;    -   rotating said at least one substrate about said axis Z-Z;    -   directing onto said at least one substrate a flow of at least        one chemical substance generated by the emission of reactant        gases and of at least one combustible gas by at least one        burner, said at least one chemical substance being suitable to        be deposited around said at least one substrate for forming at        least one preform;    -   sucking the non-deposited part of said at least one chemical        substance through at least one suction element arranged on the        opposite side to said at least one substrate with respect to        said at least one burner;    -   moving said at least one burner and said at least one suction        element parallel to said axis Z-Z;        characterised in that said step of moving said at least one        burner and said at least one suction element comprises the step        of keeping said at least one burner and said at least one        suction element on two different levels.

Preferably, said step of moving said at least one burner and said atleast one suction element comprises the step of varying the differencein level between said at least one burner and said at least one suctionelement.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention willbecome clearer from the following detailed description of some preferredembodiments, made with reference to the attached drawings. In suchdrawings:

FIG. 1 is a schematic perspective view of a device according to thepresent invention;

FIG. 2 is a schematic perspective view of the inside of the device ofFIG. 1, in a first embodiment thereof;

FIG. 3 is a schematic perspective view of the inside of the device ofFIG. 1, in a second embodiment thereof;

FIG. 4 is a schematic perspective view from below of a central portionof the inside of the device of FIG. 1 in the embodiment of FIG. 2 andfrom a point of view opposite to that of FIGS. 1 and 2;

FIG. 5 is a schematic perspective view of the inside of the device ofFIG. 1 with some of its constructive elements removed, from a point ofview opposite to that of FIG. 1;

FIG. 6 is a schematic perspective view of a side portion of the deviceof FIG. 1, from a first point of view;

FIG. 7 is a schematic perspective view of the side portion of FIG. 6,from a second point of view opposite to that of FIG. 6;

FIG. 8 is a schematic side view of the inside of the device of FIG. 1,in an alternative embodiment thereof.

DETAILED DESCRIPTION OF THE INVENTION

In such figures, with numeral reference 1 is indicated a device formanufacturing one or, preferably more (for example, in the specific casedescribed and illustrated here, four) preforms of glass material foroptical fibres in accordance with the present invention. Such a deviceis suitable for carrying out a simultaneous chemical deposition, througha process of the OVD (Outside Vapor Deposition) type, on a predeterminednumber of cylindrical supports (for example, in the specific casedescribed and illustrated here, four) each constituting a substrate forchemical deposition for the realisation of a respective preform.

The device 1 comprises an external unit 2, preferably with rectangularwalls, inside of which is defined a chemical deposition chamber 3. Theunit 2 is internally coated with sheets of fibreglass which guaranteeexcellent resistance to the acid attack (which occurs during chemicaldeposition) and to the temperature.

In chamber 3 three different sections are defined: a first side section3 a, a central section 3 b and, on the opposite side to the first sidesection 3 a with respect to the central section 3 b, a second sidesection 3 c.

The first side section 3 a houses a plurality of burners 4 (for example,in the specific case described here, four, only one of which beingillustrated) of the conventional type, each of which is adapted to blowa chemical substance for forming a preform, in particular a mixture ofsilicon and germanium in the form of oxides (SiO₂ and GeO₂), on arespective cylindrical support 4 a (of which, as shown in FIG. 4, onlythe ends are visible), so as to manufacture, at the end of the processof chemical deposition, a preform 400.

Alternatively, for each cylindrical support 4 a two or more burners,placed one above the other or one next to the other, can be provided.

The central section 3 b houses the cylindrical supports 4 a for preformformation. Such supports are arranged in suitable gripping members whichcan be provided directly inside the chamber (integrally connected withthe unit 2) or, as in the preferred embodiment illustrated in theattached figures, on a carriage 5 (shown alone in FIG. 4) which can beremoved from the unit 2 of the device 1; the carriage is structurallydisconnected from the unit 2 and is intended to be associatedco-operatively with it when fully inserted in the chamber 3.

The second side section 3 c houses a plurality of suction elements 6(for example, in the specific case described and illustrated here, fourhoods), each of which being adapted to collect and discharge the exhaustchemical substances produced by the burners 4 from the chemicaldeposition chamber 3.

The sections 3 a, 3 b and 3 c follow each other in the chemicaldeposition chamber 3 along a horizontal direction X; in the chamber 3are then defined a horizontal direction Y, substantially perpendicularto the direction X, which constitutes the insertion/removal direction ofthe carriage 5 into/from the chamber 3, and a vertical direction Z,which constitutes the positioning direction of the cylindrical supports4 a in the chamber 3 during the chemical deposition process.

In its working configuration, illustrated in FIG. 2, the device of thepresent invention exhibits the carriage 5, with the cylindrical supports4 a already loaded, fully inserted in the central section 3 b of thechemical deposition chamber 3. In such a configuration, each of thecylindrical supports 4 a is lined up along direction X and situatedbetween a corresponding burner 4 and a corresponding suction hood 6.

The unit 2 of the device of the invention comprises a frontal side wall7 (according to the point of view of FIG. 2) extended perpendicularly tothe direction Y and centrally provided with an opening 7 a to allow theinsertion and removal, along the direction Y, of the carriage 5 in andfrom the central section 3 b of the chemical deposition chamber 3.Moreover, the unit 2 comprises a rear side wall 8 (according to thepoint of view of FIG. 2) extended parallel to the wall 7.

The carriage 5 comprises a frontal side surface 9 (according to thepoint of view of FIG. 2) of a form which is conjugate to that of theopening 7 a and adapted to close this opening when the carriage 5 isfully inserted in the chamber 3. The carriage 5, moreover, comprises arear side surface 10 (according to the point of view of FIG. 2) parallelto surface 9 and equipped, above and below, with a pair of abutmentelements 15 (visible in FIGS. 3 and 4) adapted to co-operate withrespective abutment elements 16 provided on the rear wall 8 of the unit2. Preferably, the abutment elements 15 are pins whereas the abutmentelements 16 are cylindrical bushes adapted to house the aforementionedpins inside of them when the carriage 5 is fully inserted in chamber 3.

As shown in FIGS. 2 to 4, the carriage 5 comprises, moreover, a pair ofrespective upper and lower ledgers 20 a, 20 b, and a pair of respectivefront and rear uprights 21 a, 21 b, (according to the point of view ofFIG. 2). On the ledgers 20 a, 20 b a plurality of pairs of grippingmembers (in the specific example described and illustrated here, fourpairs) are rotatably mounted. Each pair of gripping members comprises apair of respective upper and lower chucks 22 a, 22 b, of theconventional type, realised, for example, in aluminium alloy (ergal);such chucks are adapted to hold opposing end portions of a respectivecylindrical support 4 a. The chucks 22 a are rotatably mounted on theupper ledger 20 a separated from each other by a predetermined distanced; in the same way, the chucks 22 b are rotatably mounted on the lowerledger 20 b separated from each other by the predetermined distance d;the chucks 22 a and 22 b of each pair of chucks are thus lined up alonga respective vertical axis Z-Z: such an axis constitutes the rotationalaxis of the chucks 22 a, 22 b and coincides with the longitudinal axisof the cylindrical support 4 a when it is positioned in the respectivechucks 22 a, 22 b.

The carriage 5 comprises a plurality of elements for moving andsupporting itself on the floor: such elements preferably comprise aplurality of spherical elements 23 of the conventional type;alternatively, the use of other elements of the conventional type, suchas rollers, spinning wheels, etc., is provided.

The spherical elements 23 are preferably associated with a base frame 24of the carriage 5; even more preferably, such spherical elements 23 aremounted at the free ends of respective front and rear arms 25 and 26,respectively (according to the point of view of FIG. 2), of the baseframe 24. In an embodiment of the carriage 5 of the present inventionwhich is not illustrated, the rear arm 26 comprises two opposing smallarms hinged upon the base frame 24 through respective spring mechanismswhich, in a rest state (carriage 5 fully removed from the chemicaldeposition chamber 3), force the small arms to open and which, when thecarriage 5 is inserted in the chamber 3, are forced to close thusallowing the full insertion of the carriage itself in the chamber 3.

For the purpose of facilitating the insertion and removal of thecarriage 5 in and from the chemical deposition chamber 3, the carriage 5preferably comprises, moreover, a plurality of sliding rollers 27associated with the upper and lower ledgers 20 a, 20 b and equipped withrespective grooves adapted to engage with respective upper and lowersliding runners 28 a, 28 b, respectively, provided in the centralsection 3 b of the chamber 3. In particular, the rollers 27 are lined upalong the longitudinal edges of the ledgers 20 a, 20 b so as to have, oneach ledger, two parallel lines of rollers. Correspondingly, in thecentral section 3 b of the chamber 3 two pair of sliding runners areprovided: a first pair 28 a, on the upper surface of the chamber 3,adapted to co-operate with the rollers associated with the upper ledger20 a of the carriage 5, and a second pair 28 b, on the lower surface ofthe chamber 3, adapted to co-operate with the runners associated withthe lower ledger 20 b of the carriage 5.

The position of the sliding rollers 27 and runners 28 a, 28 b can,however, be reversed, with the rollers 27 mounted on the upper and lowersurfaces of the chamber 3 and the runners 28 a, 28 b provided on thecarriage 5; alternatively, a mixed system of rollers and runners both onthe carriage and in the chamber can be provided.

In a first alternative and not illustrated embodiment of the device ofthe present invention, the carriage 5 does not comprise the slidingrollers 27 and the chemical deposition chamber 3 does not comprise thesliding runners 28 a, 28 b; in such an embodiment the correctpositioning of the carriage 5 in the chemical deposition chamber 3depends exclusively upon the abutment elements 15 and 16 mentionedabove.

In a second alternative and not illustrated embodiment of the device ofthe present invention, the sliding runners 28 a, 28 b are of thetelescopic type and can be extracted from the chemical depositionchamber 3; in such an embodiment, the carriage 5 does not comprise themembers for transportation on the floor (spherical elements 23): theremoval and the insertion of the carriage 5 from and in the chemicaldeposition chamber 3 can indeed rely exclusively upon the slidingrunners 28 a, 28 b and the rollers 27. The movement of the carriage 5outside of the chemical deposition chamber can be achieved by providing,on the ceiling or the floor of the room which houses the device of theinvention, a suitable system of rails or sliding runners for the rollers27 of the carriage 5.

The structure of the carriage 5 (in particular the two ledgers 20 a, 20b and the two uprights 21 a, 21 b) is preferably realised in anodisedhard aluminium alloy (anticorodal), with an anodisation thicknesspreferably of about 30-80 μm, more preferably of about 60 μm. The use ofan anodised aluminium alloy allows a good resistance to corrosion byacids, which could show up after chemical deposition, to be achievedtogether with lightness and low cost (with respect, for example, tostainless steel).

Preferably, a handle (not illustrated) is associated with the frontsurface 9 of the carriage 5 to facilitate the insertion/removalmanoeuvres in/from the chamber 3 and its movements outside of thechamber. One or more inspection windows (not shown) are provided, forexample, on the side surface 9 of the carriage 5 and/or on the wall 8 ofthe unit 2. A door of access to the chamber 3 can, moreover, be providedin the wall 8 of the unit 2, at the section 3 a, 3 b or 3 c.

The rotation of the cylindrical supports 4 a about the respectiverotational axes Z-Z during the process of chemical deposition takesplace by operating the rotation of at least one of the chucks 22 a, 22b; in accordance with the embodiments illustrated in the attachedfigures, the upper chucks 22 a are driven, while the lower chucks 22 bare mounted idle on the lower ledger 20 b of the carriage 5. For such apurpose, the device 1 of the invention comprises a motor 30 and a firstkinematic chain 30 a placed between the motor 30 and the chucks 22 a,illustrated in detail in FIG. 2. Alternative embodiments of the deviceof the present invention can be provided wherein both the upper andlower chucks 22 a, 22 b or only the lower chucks 22 b are controlled torotate.

In a first embodiment of the device of the present invention,illustrated in FIGS. 2 and 4, the motor 30 is preferably housed in theupper part of the central portion 3 b of the chamber 3. The kinematicchain 30 a comprises an angular transmission member 31 kineticallyassociated with the motor 30 and with a horizontal countershaft 32 whichextends along direction Y; such a countershaft 32 is kineticallyassociated with a plurality of 90° angular transmission members 33 (forexample, in the specific case described and illustrated here, fourtransmission members). Each angular transmission member 33 is in turnkinetically associated with a vertical countershaft 330 (only partiallyvisible in FIG. 4) upon which a toothed wheel 34 is force fitted. Eachwheel 34 engages, when the carriage 5 is fully inserted in the chemicaldeposition chamber 3, with a corresponding toothed wheel 35 arranged onthe upper surface of the upper ledger 20 a of the carriage 5; this wheelis integrally connected and coaxial with the chuck 22 a.

In an alternative embodiment of the device of the present invention,illustrated in FIG. 3, the horizontal countershaft 32 is integrallyconnected with the carriage 5 and comprises, on one of its free ends, aconical or alternatively toothed clutch 36, adapted to be kineticallyassociated, when the carriage is fully inserted in the chemicaldeposition chamber, with a corresponding sleeve 37 integrally connectedwith the motor 30. A plurality of 90° angular transmission members 33(for example, in the specific case described and illustrated here, fourtransmission members) are kinetically associated to the shaft 32. Eachangular transmission member 33 is in turn kinetically associated with avertical countershaft 38 which is substantially coaxial to therotational axis Z-Z of the cylindrical supports 4 a.

In a further embodiment (not shown) of the device of the presentinvention, all the members for moving the preforms (motor 30 andkinematic chain 30 a) are integrated in the carriage 5, which isarranged to allow an electrical connection for the power supply.

As already mentioned, the unit 2 houses, at section 3 a of the chemicaldeposition chamber 3, four burners 4. Such burners are placed at thepredetermined distance d from each other so that they are lined up alongthe direction X with the cylindrical supports 4 a when the carriage 5 isfully inserted in the chamber 3.

During the process of chemical deposition, the burners 4 move togetheralong the vertical direction Z (which is parallel to the longitudinalaxes Z-Z of the cylindrical supports 4 a), preferably with differentspeeds in the working stroke (which, preferably, is an upwards stroke)and the return stroke (downwards stroke) . The direction of the workingand return strokes can, however, be reversed.

The burners 4 are, moreover, preferably capable of moving towards/awayfrom the supports 4 a along the direction X. Such a motion allows thedistance between the burners 4 and the side surfaces of the preforms 400in formation to be controlled, so that, for example, during the chemicaldeposition, it always maintains a predetermined value, so as to controlthe temperature of the side surface of the preforms in formation (such atemperature would indeed tend to change due to the fact that, when thepreform grows, the distance between the burners 4 and the side surfaceof the preform would tend to decrease).

The movement of the burners along the directions X and Z can also beused, advantageously, during the maintenance operations to facilitatethe assembly and disassembly of the burners themselves and/or the entry(should the possible door of access be provided at the section 3 a) andthe mobility of the operators inside the chamber 3.

The burners 4 are positioned in such a way as to emit the flow ofreactants along a direction substantially perpendicular to the axis Z-Zof the cylindrical supports 4 a. The burners 4 are mounted on respectiveplates 40 equipped, at the centre, with a preferably circular hole 41 toallow the easy connection to the burner of the gas feeding tubes 39coming from outside of the unit 2.

The burners 4 are associated with a system suitable for allowing theirmovement, in the vertical direction Z and in the horizontal direction X,towards or away from the cylindrical supports 4 a. The FIGS. 2, 3 and 5illustrate a first embodiment of such a system for moving the burnersalong the directions X and Z; FIG. 8 illustrates a second embodiment ofthe aforementioned system for moving the burners.

In accordance with the embodiment illustrated in FIGS. 2, 3 and 5, theplates 40 are mounted on a pair of ledgers 42 which are substantiallyhorizontal and integrally attached the one with the other.

Preferably, the construction material of the plates 40 and of theledgers 42 is, as said with respect to the carriage 5, an anodised hardaluminium alloy (anticorodal); this allows to achieve the aforementionedadvantages of resistance to corrosion by acids (which can show up afterchemical deposition), of lightness and of low cost.

The system for moving the burners in the vertical direction Z comprisesa motor 50 and a kinematic chain 50 a placed between the motor 50 andthe ledgers 42.

The motor 50 is preferably placed outside of the chamber 3, at thesection 3 a, in the upper part of a wall 11 of the unit 2 substantiallyperpendicular to the wall 7. The kinematic chain 50 a comprises a doubleangular transmission member 51 kinetically associated with the motor 50and, placed in a mirror-like arrangement on opposite sides with respectto the double angular transmission member 51, a pair of countershafts 52a, 52 b extended horizontally along the direction Y. Each of the shafts52 a, 52 b is in turn kinetically associated with a 90° angulartransmission member 53 a, 53 b which transfers the motion to acorresponding grooved shaft 54 a, 54 b extended inside the chamber 3,along the direction X, in the upper part of the section 3 a. Eachgrooved shaft 54 a, 54 b is kinetically associated (through a slidingsleeve which cannot be seen in the figures) with a 90° angulartransmission member 55 a, 55 b which transfers the motion to a verticalballscrew 56 a, 56 b; the pair of ledgers 42 for supporting the burnersis then associated with each screw 56 a, 56 b through a nut screw (notillustrated). Through the aforementioned kinematic chain, the motionimparted by the motor 50 is transferred to the ballscrews 56 a, 56 b andis converted into the movement along the direction Z of the ledgers 42and, therefore, of the burners associated with them. The translationalmotion is guided along the direction Z by a pair of vertical slidingrunners 57 a, 57 b, associated with the ledgers 42 for supporting theburners and extended parallel and adjacent to the screws 56 a, 56 b.

In other words, the vertical ballscrews 56 a, 56 b are assigned thefunction of pushing the ledgers 42, while the vertical runners 57 a, 57b are assigned the function of guiding such a movement. There are twoscrews 56 a, 56 b in order to balance out the thrust.

The movement of the burners in the horizontal direction X towards oraway from the cylindrical supports 4 a takes place by controlling themovement along such a direction of the ballscrews 56 a, 56 b and of therunners 57 a, 57 b (and, therefore, of the ledgers 42 for supporting theburners which are associated with them). For such a purpose, the device1 of the invention comprises a motor 60 and a kinematic chain 60 aplaced between the motor and the ballscrews 56 a, 56 b.

The motor 60 is preferably placed outside of the chamber 3, at thesection 3 a, in the lower part of the wall 11. The kinematic chain 60 acomprises a double angular transmission member 61 kinetically associatedwith the motor 60 and, positioned in a mirror-like arrangement onopposite sides with respect to the double angular transmission member61, a pair of transmission countershafts 62 a, 62 b extendedhorizontally along the direction Y. Each of the shafts 62 a, 62 b is inturn kinetically associated with a 90° angular transmission member 63 a,63 b which transfers the motion to a corresponding ballscrew 64 a, 64 bextended along the direction X in the lower part of the section 3 a ofthe chamber 3. Each angular transmission member 63 a, 63 b transfers,moreover, the motion to a vertical shaft 65 a, 65 b which is kineticallyassociated with a 90° angular transmission member 66 a, 66 b positionedin the upper part of the wall 11. Such a transmission member transfersthe motion to a ballscrew 67 a, 67 b which extends in the upper part ofthe inside of the chamber 3 along the direction X.

On each of the lower screws 64 a, 64 b a block is engaged (through alead nut which cannot be seen in the figures) which moves in thedirection X when the aforementioned screws turn. Each of the upperscrews 67 a, 67 b is associated (through a nut screw which cannot beseen in the figures), to the angular transmission member 55 a, 55 bwhich moves in the direction X when the aforementioned screws turn.Moreover, the vertical screws 56 a, 56 b and the vertical runners 57 a,57 b are associated with the blocks 68 a, 68 b. The translational motionis guided along the direction X by a pair of horizontal sliding runners69 a, 69 b associated with the blocks 68 a, 68 b and extended paralleland adjacent to the screws 64 a, 64 b.

In other words, the lower and upper horizontal ballscrews 64 a, 64 b and67 a, 67 b respectively are assigned the function of pushing thevertical ballscrews 56 a, 56 b and the runners 57 a, 57 b (and, thus,the ledgers 42 for supporting the burners which are associated to them),while the horizontal runners 69 a, 69 b are assigned the function ofguiding such movement. There are four screws 64 a, 64 b and 67 a, 67 b,two above and two below, in order to balance out the thrust.

All the screws and the runners mentioned above are protected from thecorrosive acidic substances, which generate during the chemicaldeposition, through bellows made of sewn and sealed Kevlar material.

As already mentioned and as shown in FIGS. 5 and 6, the unit 2 houses,at the section 3 c of the chemical deposition chamber 3, four suctionhoods 6. The hoods are positioned at a predetermined distance d fromeach other so as to be arranged in front of the cylindrical supports 4on the opposite side with respect to the burners when the carriage 5 isfully inserted in the chamber 3.

The suction hoods 6 move all together, during the process of chemicaldeposition, along the vertical direction Z (i.e. parallel to thelongitudinal axis Z-Z of the cylindrical supports 4 a).

The hoods 6, during their motion, are placed at a different level tothat of the burners in order to optimise the fluid dynamic effects inthe area surrounding each cylindrical support 4 a and to facilitate thecollection and discharge of exhaust gases. More preferably, the hoods 6are placed at a lower level with respect to the burners and remainalways at a lower level during the whole process of chemical deposition.By keeping the hoods 6 at a lower level with respect to the burners 4,the suction current generated by the hoods themselves tends to opposethe rising effect of the gases caused by the high temperatures, thuskeeping the flow of such gases substantially horizontal in theinteraction with the preform in formation.

Advantageously, the provision of a suction hood downstream from thepreform along the fluid dynamic path of the gases and reactants and thepositioning of the hood at a lower level with respect to that of theburner allows an impact direction of the gas flow on the preform whichis substantially perpendicular to the axis of the preform to bemaintained. In substance, such an arrangement allows the detachment ofthe laminar boundary layer (the meaning of which is known in thermalfluid dynamics) from the surface of the preform to be delayed: in such away, advantageously, an increase in the yield of the process of chemicaldeposition and an improvement of the characteristics of compactness anduniformity of the preform is achieved.

The motion of the hoods 6 in the direction Z can be synchronised withthe motion of the burners, or else, for particular reasons of fluiddynamic optimisation, it is possible to provide for a motion which isdifferent (not synchronised) with respect to that of the burners, and,that is, to provide for a variation in the difference in level betweenthe hoods and the burners; this is allowed by the fact that the systemsfor moving the hoods and the burners are independent, as describedbelow. Such a variation in level can be required to compensate thevariations in temperature which occur inside the chamber 3, or else tocompensate the variation of one or more of the parameters of thedeposition process. For example, if during the process the flow rate ofthe reactant gases needs to be increased, the difference in levelbetween the hoods and the burners is increased to increase the suckingeffect towards the bottom generated by the hoods, thus ensuring that theimpact trajectory of the gas flow with the preform in formation issubstantially perpendicular.

The hoods 6 are preferably associated with a substantially horizontalsupporting ledger (not illustrated) and can be oriented manually. Such aledger, moreover, supports a substantially horizontal collector tube 70for collecting and discharging chemical substances and the particulategenerated in the chamber 3 during chemical deposition. The tube 70 is inturn in fluid communication with an exhaust chamber 71 (FIGS. 6 and 7)through an exhaust opening 8 a formed on a side portion of the wall 8 ofthe unit 2; this chamber is adapted for taking the exhaust gases to ascrubber, through a heat-resistant tube 72.

The collector tube 70 exhibits a section which is variable andprogressively growing as it approaches the exhaust opening 8 a.

The ledger supporting the hoods 6 and the collector tube 70 isassociated with a first system suitable for allowing the movement of theledger itself (and thus of the hoods associated with it) in the verticaldirection Z and with a second system suitable for allowing the movementof the ledger itself (and thus of the hoods associated with it) in thehorizontal direction X towards/away from the cylindrical supports 4 a.Such systems are substantially identical and specular to those describedabove which allow the movements along the direction X and Z of theburners; they are, moreover, kinetically independent from these othersystems so as to be able to separately and independently control themotion of the burners and the motion of the hoods (such motions, asalready stated, can be synchronised or, for reasons of fluid dynamicoptimisation, non-synchronised).

The FIGS. 2, 3, 6 and 7 illustrate a first embodiment of the systems formoving the hoods 6 along the directions X and Z; FIG. 8 illustrates asecond embodiment of the aforementioned systems for moving the hoods.

In accordance with the embodiment illustrated in FIGS. 2, 3, 6 and 7,the movement of the hoods 6 in the vertical direction Z takes place bycontrolling the movement of the ledger supporting the hoods and thecollector tube. For such a purpose, the device 1 of the inventioncomprises a motor 80 and a kinematic chain 80 a placed between the motor80 and the ledger supporting the hoods and the collector tube (see inparticular FIGS. 6 and 7).

The motor 80 is preferably placed outside of the chamber 3, at thesection 3 c, in the upper part of a wall 12 of the unit 2 substantiallyparallel with the wall 11. The kinematic chain 80 a comprises a doubleangular transmission member 81 kinetically associated with the motor 80and, placed in a mirror-like arrangement on opposite sides with respectto the double angular transmission member 81, a pair of transmissioncountershafts 82 a, 82 b extended horizontally along the direction Y.Each of the shafts 82 a, 82 b is in turn kinetically associated with a90° angular transmission member 83 a, 83 b which transfers the motion toa corresponding grooved shaft 84 a, 84 b extended along the direction Xin the upper part of the section 3 c, inside the chamber 3. Each groovedshaft 84 a, 84 b is kinetically associated (through a sliding sleevewhich cannot be seen in the figures) with a 90° angular transmissionmember 85 a, 85 b which transfers the motion to a vertical ballscrew 86a, 86 b; the ledger for supporting the hoods and the collector tube isthen associated with each screw 86 a, 86 b through a nut screw (notshown). Through the aforementioned kinematic chain, the motion impartedby the motor 80 is transferred to the ballscrews 86 a, 86 b andconverted into movement along the direction Z of the ledgers forsupporting the hoods and the collector tube. The translational movementis guided along the direction Z by a pair of vertical sliding runners 87a, 87 b, extended parallel and adjacent to the screws 86 a, 86 b.

In other words, the vertical ballscrews 86 a, 86 b are assigned thefunction of pushing the ledger supporting the hoods 6 and the collectortube 70, while the vertical runners 87 a, 87 b are assigned the functionof guiding such movement. There are two screws 86 a, 86 b in order tobalance out the thrust.

The movement of the hoods 6 in the horizontal direction X towards oraway from the cylindrical supports 4 a occurs by controlling themovement along such a direction of the ballscrews 86 a, 86 b and of therunners 87 a, 87 b (and, therefore, of the ledger supporting the hoodsand the collector tube which is connected to them). For such a purpose,the device 1 of the invention comprises a motor 90 and a kinematic chain90 a placed between the motor 90 and the assembly of the ballscrews 86a, 86 b and the guides 87 a, 87 b.

The motor 90 is preferably placed outside of the chamber 3, at thesection 3 c, in the lower part of the wall 12. The kinematic chain 90 acomprises a double angular transmission member 91 kinetically associatedwith the motor 90 and, arranged in a mirror-like arrangement on oppositesides with respect to the double angular transmission member 91, a pairof countershafts 92 a, 92 b extended horizontally along the direction Y.Each of the shafts 92 a, 92 b is in turn kinetically associated with a90° angular transmission member 93 a, 93 b which transfers the motion toa corresponding ballscrew 94 a, 94 b extended along the direction X andplaced in the lower part of the section 3 a, inside the chamber 3 (FIG.6). Each angular transmission member 93 a, 93 b transfers, moreover, themotion to a vertical shaft 95 a, 95 b which is kinetically associatedwith a 90° angular transmission member 96 a, 96 b positioned in theupper part of the wall 12. Such a transmission member transfers themotion to a ballscrew 97 a, 97 b which extends in the upper part of theinside of the chamber 3 along the direction X.

A block 98 a is engaged on each of the lower screws 94 a, 94 b (througha lead nut which cannot be seen in the figures). Such block moves in thedirection X when the aforementioned screws turn. Each of the upperscrews 97 a, 97 b is associated (through a nut screw which cannot beseen in the figures), with the angular transmission member 85 a, 85 bwhich moves in direction X when the aforementioned screws turn.Moreover, the vertical screws 86 a, 86 b and the vertical runners 87 a,87 b are associated with the blocks 98 a, 98 b. The translational motionis guided along the direction X by a pair of horizontal sliding runners99 a, 99 b associated with the blocks 98 a, 98 b and extended paralleland adjacent to the screws 94 a, 94 b.

In other words, the lower and upper horizontal ballscrews 94 a, 94 b and97 a, 97 b respectively are assigned the function of pushing thevertical ballscrews 86 a, 86 b and the runners 87 a, 87 b (and,therefore, the ledger for supporting the hoods 6 and the collector tube70 associated with them), while the horizontal runners 99 a, 99 b areassigned the function of guiding such movement. There are four screws 94a, 94 b and 97 a, 97 b, two above and two below, in order to balance outthe thrust.

All of the screws and runners mentioned above are protected, from thecorrosive acidic substances which generate during chemical deposition,through bellows (not illustrated) in sewn and sealed Kevlar fabric.

As already stated, FIG. 8 illustrates an alternative embodiment of thesystems for moving the burners 4 and hoods 6 along the directions X andZ. In accordance with such an embodiment, the movement of the burnersalong the horizontal direction X is realised by associating the burners4 with a first vertical plate 43 a which is mobile, for example throughtelescopic runners 44 a, with respect to a second vertical plate 45 a.The movement of the burners along the vertical direction Z is realisedby associating the second vertical plate 45 a with a pair of verticalrunners 46 a through sliding blocks 47 a. In the same way, the movementof the hoods 6 along the horizontal direction X is realised byassociating the hoods 6 with a first vertical plate 43 b which ismobile, for example through telescopic runners 44 b, with respect to asecond vertical plate 45 b. The movement of the hoods 6 along thevertical direction Z is realised by associating the second verticalplate 45 b with a pair of vertical runners 46 b through sliding blocks47 b.

Alternatively, instead of a single plate 43 a and a single plate 45 awhich support all of the burners 4, a plurality of plates 43 a and aplurality of plates 45 a, each associated with a respective burner canbe provided. This allows independence of movement for individualburners. The same can be realised for the plates 43 b and 45 b.

As already stated, the collector tube 70 is associated with the wall 8of the unit 2, where it inserts into the exhaust chamber 71 at theexhaust opening 8 a (FIGS. 5 and 6). In order to allow the movement inthe direction X and Z of the collector tube in section 3 c of thechamber 3 with respect to the wall 8, the device 1 of the inventionpreferably comprises a sliding coupling between the collector tube 70and the wall 8.

In accordance with a first embodiment (illustrated in the attachedfigures) of the device of the present invention, such a coupling takesplace, preferably, according to the following conditions: the portion ofwall 8 in proximity of the collector tube 70 is defined by a pair ofrespective upper and lower, with respect to the collector tube 70,vertical tapes 73 a, 73 b which can slide in the direction Z. The tapes73 a, 73 b are preferably made from stainless steel and are integrallyassociated, at the respective free ends, with an intermediate plate 74which exhibits a central slot 75 (seen in FIG. 6) extended along thedirection X for a length equal to or greater than the stroke of thecollector tube 70 towards/away from the cylindrical supports 4 a. Afurther plate defining a flange 76 (shown in FIG. 5 but not in FIG. 6 toallow the plate 74 to be seen) is integrally associated with the tube70. The flange 76 is preferably realised in teflon.

The flange 76 faces the plate 74 towards the inside of the chamber andis larger than the slot 75 in order to close such a slot even when thecollector tube 70 is at its end (base stroke position along thedirection X); in this way the chemical deposition chamber 3 is fluiddynamically connected to the exhaust chamber 71 just through thecollector tube 70 which inserts into the chamber 71 at the opening 8 aformed in the flange 76. The plate 74 preferably exhibits runners forthe horizontal movement of the flange 76. The flange 76 canalternatively face the plate 74 towards the outside of the chamber, orelse the plate 74 can exhibit a seat inside of which the flange 76 isfree to slide.

The tapes 73 a, 73 b are associated with respective winding/unwindingrollers (not shown); such rollers are positioned inside suitable boxes77 a, 77 b mounted on the wall 8 of the unit 2, above and below,respectively, the rollers themselves. When the collector tube 70 rises,the upper tape 73 a winds up on the roller positioned in the upper box77 a, while the lower tape 73 b unwinds from the roller positioned inthe lower box 77 b, and vice versa. The winding of the tapes on therollers is made easier by the presence of a winding spring in each ofthe two boxes 77 a, 77 b.

The movement in direction Z of the collector tube 70 is, therefore,allowed by the sliding in direction Z of the tapes 73 a, 73 b; themovement in direction X, on the other hand, is allowed by the sliding indirection X of the flange 76 with respect to the two tapes 73 a, 73 b.

Preferably, the construction material of the hoods 6, of the collectortube 70 and of the ledger supporting the hoods and tube is an anodisedhard aluminium alloy (anticorodal); this allows the advantages ofresistance to acid corrosion (which can show up after chemicaldeposition) and of lightness and low cost mentioned above to beachieved.

To move the plate 74, and thus the collector tube 70, in direction Z,instead of the tape system, a system using “bellows” elements (notshown) can be used. In practice, the tapes 73 a and 73 b can be replacedwith a first and a second “bellows” element which support the plate 74from above and below and define respective lower and upper portions (ofvariable extension) of the wall 8.

As a further possible alternative, instead of a system of tapes or usingbellows elements, a non-sealed system can be used, such as a systemcomprising two series of opposing horizontal bristles extending from theopposite sides to the space defining the aforementioned side portion ofthe wall 8 defined in proximity of the collector tube 70. In this way,the bristles slightly overlap at the centre-line of the space. Theflexibility of the bristles allow them to open and close as thecollector tube passes through thus allowing the movement of the tube indirection Z and X. Although such a system does not guarantee a sealingof the inside of the chemical deposition chamber, it is advantageoussimply from the constructive and economic point of view: moreover, thelack of a seal is not critical in that most of the exhaust gases aresucked in and discharged through the collector tube 70.

With reference to FIGS. 1 and 5, the wall 11 of the unit 2, i.e. thewall situated behind the burners, exhibits, in its upper part, suitableopenings 110 where respective pipe fittings (bulk-heads) are positioned,such pipe fittings being suitable for connecting rigid external tubes(not illustrated) for feeding gas to the chamber to flexible internaltubes (only one of which is represented, indicated with 39) fortransferring gas to the burners. In practice, a flexible tube 39 isconnected to each burner for each combustion gas and for each reactantgas.

The wall 11 exhibits, moreover, a plurality of air suction members 100(preferably a number equal to the number of burners) to provide into thechamber 3 an air flow adapted to replace the air discharged by thesuction hoods 6.

The air suction members 100 extends along a portion of the wall 11, inproximity of the single burners, and are mobile in direction Z with amotion which is synchronised with respect to that of the burners, so asto be substantially at the same level as the burners during the wholedeposition process.

Preferably, the wall 11 comprises a system of sliding tapes similar tothose described with reference to the sliding coupling between thecollector tube 70 and the wall 8, to allow the motion along thedirection Z of the air suction members 100. In particular, the wall 11comprises a wide central portion which consists of a pair of respectiveupper and lower vertical tapes 11 a, 11 b with respect to the airsuction members 100. Such tapes can be made from rubberised fabric,teflon, metal (preferably steel) and are integrally associated, at therespective free ends, with an intermediate plate 111. Such a plateexhibits, in proximity of the burners, a plurality of openings definingthe aforementioned air suction members 100. Preferably, the plate 111 isintegrally connected with the ledgers 42 for supporting the burners, sothat the air suction members 100 are kinetically associated with theburners 4. The air suction members 100 can be, for example, rectangular,and can have a height of around 35-40 cm.

The tapes 11 a, 11 b are associated with respective winding/unwindingrollers (not shown) housed inside suitable boxes 112 a, 112 b (FIG. 5)mounted on the upper and lower part of the wall 11, respectively. Whenthe ledgers 42 rise, the upper tape 11 a winds up on the rollerpositioned in the upper box 112 a while the lower tape 11 b unwinds fromthe roller positioned in the lower box 112 b and vice versa. The windingof the tapes on the rollers is made easier by the presence of respectivewinding springs.

To move the plate 111, instead of a tape system, a system of “bellows”elements (not shown) can be used. In practice, the tapes 11 a and 11 bcan be replaced by a first and a second “bellows” element, which supportthe plate 111 from above and below and define the respective lower andupper portions (of variable extension) of the wall 11.

More generally, the air suction members 100 can be formed in any elementwhich can be controllably moved in direction Z along the wall 11, forexample through a runner-slide moving system. Such a moving system canbe associated with the system for moving the ledgers 42, or can beindependent.

As a further possible alternative, instead of a plurality of air suctionmembers, there can be a single air suction member, having a horizontalextension substantially equal to that of the row of burners 4. In thesame way as the case of a plurality of air suction members, the singleair suction members can be formed in a plate associated with a pair oftapes which slide in the direction Z. Alternatively, the air suctionmembers can be formed in any other element which is capable of movingvertically along the direction Z.

The device 1 comprises, moreover, a unit for feeding gas and reactants(not illustrated) positioned outside of the chemical deposition chamber3 and an electric control board (not shown) for controlling the rotationof the preform and the movement of the burners 4 and the hoods 6 alongthe directions X and Z. Preferably, the unit for feeding gas andreactants and the electric control board are controlled by a centralisedcontrol unit (not illustrated).

In operation, with reference to the embodiment of the device of theinvention illustrated in the attached figures, the cylindrical supports4 a are loaded onto the carriage 5 outside of the chemical depositionchamber 3 and, possibly, in a position away from it. The carriage 5 withthe supports loaded is then inserted in the chamber 3; such an insertionis made easier by the presence of the sliding rollers 27 which engagewith the sliding runners 28 a, 28 b. When the carriage is fully insertedin the chamber 3, the toothed wheels 34, kinetically associated with themotor 30 through the kinematic chain 30 a, engage with the toothedwheels 35 placed on the upper ledger 20 a of the carriage 5; theactuation of the motor 30 then operates the rotation of the cylindricalsupports 4 a and the process of chemical deposition can thus begin.During such a process the burners 4 and the hoods 6 move along thevertical direction Z and the horizontal direction X through the motiontransmission members 50 a, 60 a, 80 a, 90 a described above, with thehoods 6 which always remain at a different height with respect to thatof the burners 4 so as to optimise the fluid dynamic conditions insidethe chamber. At the end of the deposition process the carriage 5 withthe preforms 400 is removed from the chamber 3 of the unit 2 and ismoved away from the unit 2, to be able to proceed to the operations ofremoval of the preforms, which will undergo the successive desiccationand consolidation steps.

1. A method for manufacturing a preform for optical fibres, comprisingthe following steps: (a) supporting at least one substrate for chemicaldeposition in a vertical position along an axis Z-Z; (b) rotating saidat least one substrate about said axis Z-Z; (c) directing onto said atleast one substrate a flow of at least one chemical substance generatedby the emission of reactant gases and of at least one combustible gas byat least one burner, said at least one chemical substance being suitableto be deposited around said at least one substrate for forming at leastone preform; (d) sucking the non-deposited part of said at least onechemical substance through at least one suction element arranged on theopposite side to said at least one substrate with respect to said atleast one burner; and (e) moving said at least one burner and said atleast one suction element parallel to said axis Z-Z; wherein the step ofmoving said at least one burner and said at least one suction elementfurther comprises the step of keeping said at least one suction elementalways at a lower height with respect to that of said at least oneburner.
 2. The method according to claim 1, wherein said step of movingsaid at least one burner and said at least one suction element furthercomprises the step of varying the difference in level between said atleast one burner and said at least one suction element.